The changelog says: "The equivalent routine for x86 is in arch/x86/kernel/process.c but the powerpc implementation is different.":

Unfortunately the changelog is completely useless as it does not tell_WHY_ it is different.

Aside of being different the implementation is patently wrong.

The rescheduling IPI is async. That means that there is no guarantee,that the other cores have executed the IPI when cpu_idle_wait()returns. But that's the whole purpose of this function: to guaranteethat no CPU uses the old idle handler anymore.

Use the smp_functional_call() based implementation, which fulfils therequirements.

[ This code is going to replaced by a core version to remove all the pointless copies in arch/*, but this one should go to stable ]Signed-off-by: Thomas Gleixner <tglx@linutronix.de>Acked-by: Peter Zijlstra <peterz@infradead.org>Cc: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>Cc: Trinabh Gupta <g.trinabh@gmail.com>Cc: Arun R Bharadwaj <arun.r.bharadwaj@gmail.com>Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>Link: http://lkml.kernel.org/r/20120507175651.980164748@linutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

/* * cpu_idle_wait - Used to ensure that all the CPUs come out of the old@@ -123,16 +126,9 @@ void cpu_idle(void) */ void cpu_idle_wait(void) {- int cpu; smp_mb();-- /* kick all the CPUs so that they exit out of old idle routine */- get_online_cpus();- for_each_online_cpu(cpu) {- if (cpu != smp_processor_id())- smp_send_reschedule(cpu);- }- put_online_cpus();+ /* kick all the CPUs so that they exit out of pm_idle */+ smp_call_function(do_nothing, NULL, 1); } EXPORT_SYMBOL_GPL(cpu_idle_wait);